The present invention relates to coloured interference pigments based on multicoated platelet-shaped substrates.
Lustre or effect pigments are employed in many areas of industry, in particular in the area of automotive paints, decorative coatings, plastics, surface coatings, printing inks and cosmetic formulations.
Lustre pigments based on transparent platelet-shaped substrates which do not have a xe2x80x9chardxe2x80x9d metallic lustre are the subject-matter of WO 93/12182. Mica platelets are covered with a high-refractive-index metal-oxide layer, such as, for example, TiO2, and a non-selectively absorbing layer. Depending on the TiO2 layer thickness, these pigments exhibit a certain interference colour when viewed perpendicularly which becomes weaker and weaker with increasingly oblique viewing angle and finally drops off to grey or black. The interference colour does not change, but a decrease in colour saturation is observed.
EP 0 753 545 A2 discloses goniochromatic lustre pigments based on multicoated, high-refractive-index, non-metallic, platelet-shaped substrates which are at least partially transparent to visible light, which pigments have at least one layer pack comprising a colourless, low-refractive-index coating and a reflective coating which absorbs selectively or non-selectively.
The multilayer pigments known from the prior art are in some cases built up from layer materials which have little or no transparency to light and can therefore only be combined with absorption pigments in a very restricted manner in use. In addition, the interference colour of these pigments is highly dependent on the viewing angle, which is undesired in the majority of applications. Furthermore, these pigments are in some cases very difficult to prepare or reproduce.
An object of the present invention is to provide coloured multilayer pigments of high tinting strength which do not have pronounced goniochromaticity, are distinguished by their advantageous applicational properties and at the same time can be prepared in a simple manner.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
Surprisingly, coloured interference pigments based on multicoated, platelet-shaped substrates have now been found on which firstly a defined absorption is produced and subsequently an interference system is defined. This combination of absorption and interference on a platelet-shaped substrate results in a coloured pigment having high colour purity of the interference colour and intense lustre.
The pigments according to the invention are distinguished over the pigments from the prior art through their extraordinarily high chroma C, their high hiding power, their high colour purity of the interference colour and high brightness. In contrast to the goniochromatic pigments from the prior art, they do not exhibit any angle dependence of the interference colour.
The invention thus relates to coloured interference pigments based on multicoated, platelet-shaped substrates, characterised in that they comprise
(A) a coloured coating having a refractive index of n greater than 1.8,
(B) a colourless coating having a refractive index of n greater than 1.8,
(C) a colourless coating having a refractive index of nxe2x89xa61.8,
(D) a colourless coating having a refractive index of n greater than 1.8, and optionally
(E) an outer protective layer.
The invention furthermore relates to the use of the interference pigments according to the invention in paints, coatings, printing inks, plastics, ceramic materials, glasses and for laser marking. Owing to the high colour strength, the pigments according to the invention are particularly suitable for decorative cosmetics. Furthermore, the pigments according to the invention are also suitable for the production of pigment preparations and for the production of dry preparations, such as, for example, granules, chips, pellets, briquettes, etc. The dry preparations are particularly suitable for printing inks, coatings and cosmetic formulations.
Suitable base substrates for the coloured pigments according to the invention are transparent platelet-shaped substrates. Preferred substrates are phyllosilicates. Particularly suitable substrates are natural or synthetic mica, talc, kaolin, platelet-shaped iron oxides or aluminium oxides, BiOCl, glass platelets, SiO2 platelets, TiO2 platelets, graphite platelets, synthetic support-free platelets, or other comparable materials. It is also possible to employ mixtures of different substrates. Particularly preferred substrate mixtures are
mica platelets+SiO2 platelets
mica platelets+Al2O3 platelets
mica platelets+glass platelets
mica platelets+TiO2 platelets
mica platelets+oxynitride platelets
mica platelets+nitride platelets
mica platelets+pearl essence
mica platelets+graphite platelets
mica platelets+BiOCl
SiO2 platelets+Al2O3 platelets
glass platelets+SiO2 platelets
The size of the base substrates is not crucial per se and can be matched to the respective application. In general, the platelet-shaped substrates have a thickness of between 0.05 and 1.5 xcexcm, in particular between 0.1 and 1 xcexcm. The extension in the two other regions is usually between 1 and 250 xcexcm, preferably between 2 and 200 xcexcm, and in particular between 5 and 60 xcexcm. It is also possible to employ substrates having different particle sizes. Particular preference is given to a mixture of mica fractions of N mica (10-60 xcexcm) and F mica (5-20 xcexcm). Preference is furthermore given to N and S fractions (10-130 xcexcm) and F and S fractions (5-130 xcexcm).
The thickness of the individual layers on the base substrate is essential for the optical properties of the pigment. Layer (A) in particular has a significant effect on the colour properties
The interference pigments according to the invention have an absorption layer (A) and an interference system (B, C, D), the latter consisting of alternating high-refractive-index layers (B, D) and low-refractive-index layer (C). The high-refractive-index layers (B) and (D) have a refractive index of n greater than 1.8, preferably nxe2x89xa72.0.
Layer (A) preferably consists of coloured oxides, sulfides, tellurides, selenides or mixed systems of these anions and of the elements from main groups 2-5 and subgroups 1, 2 and 4-8, furthermore the lanthanides and actinides. Layer (A) particularly preferably consists of Fe2O3, Fe3O4, Ce2O3, Cr2O3, Ti suboxides (TiO2 partially reduced with oxidation states of from  less than 4 to 2 and lower oxides, such as Ti3O5, Ti2O3 up to TiO), titanium oxynitrides and titanium nitride, molybdenum oxides, CoO, Co3O4, VO2, V2O3, NiO, MoS2, WS2, V2O5, CuO, Cu2O, Ag2O, CeO2, MnO2, Mn2O3, Mn2O5 or mixtures or combinations (mixed oxides) thereof. Layer (A) particularly preferably consists of Fe2O3, Fe3O4, furthermore of Cr2O3, CoO, Co3O4, VO2, V2O3, NiO, MoS2, WS2, V2O5, CuO, CeO2, Ce2O3, MnO2, Mn2O3 and/or Ag2O.
Layers (B) and (D) preferably consist of TiO2, ZrO2, SnO2, ZnO or BiOCl. Layers (B) and (D) are particularly preferably a TiO2 layer. The TiO2 here can be in the rutile or anatase modification, preferably rutile.
Materials which are suitable as colourless, low-refractive-index materials for coating (C) are preferably metal oxides or the corresponding oxide hydrates, such as, for example, SiO2, Al2O3, AlO(OH), B2O3, MgF2, MgSiO3, or a mixture of the said metal oxides. Layer (C) preferably consists of SiO2, MgF2, Al2O3 or mixtures thereof.
It is advantageous for the optical properties of the pigments according to the invention if layer (A) is very thin. The thickness of layer (A) is preferably from 1 to 100 nm, in particular from 1 to 50 nm and particularly preferably from 5 to 20 nm.
The thickness of layers (B) and (D) is preferably from 20 to 250 nm, in particular from 25 to 180 nm and particularly preferably from 40 to 150 nm. The layer thicknesses of layers (B) and (D) may be identical or different. They preferably have similar or identical layer thicknesses.
The thickness of layer (C) is preferably from 20 to 200 nm, in particular from 30 to 180 nm and particularly preferably from 40 to 150 nm.
The coating of the substrates with an absorption layer (A) and with a high-refractive-index layer (B), a low-refractive-index layer (C) and a further, colourless, high-refractive-index layer (D) results in the formation of coloured interference pigments whose colour, lustre and hiding power can be varied within broad limits.
Particularly preferred interference pigments have the following layer sequences:
substrate+Fe2O3 (A)+TiO2 (B)+SiO2 (C)+TiO2 (D)
substrate+Fe3O4 (A)+TiO2 (B)+SiO2 (C)+TiO2 (D)
substrate+Fe2O3 (A)+TiO2 (B)+Al2O3 (C)+TiO2 (D)
substrate+Fe3O4 (A)+TiO2 (B)+Al2O3 (C)+TiO2 (D)
substrate+V2O5 (A)+TiO2 (B)+SiO2 (C)+TiO2 (D)
substrate+MnO2 (A)+TiO2 (B)+SiO2 (C)+TiO2 (D)
substrate+MnO2 (A)+TiO2 (B)+Al2O3 (C)+TiO2 (D)
substrate+Ag2O (A)+TiO2 (B)+SiO2 (C)+TiO2 (D)
substrate+Ag2O (A)+TiO2 (B)+Al2O3 (C)+TiO2 (D)
substrate+CoO (A)+TiO2 (B)+SiO2 (C)+TiO2 (D)
substrate+Cr2O3 (A)+TiO2 (B)+SiO2 (C)+TiO2 (D)
substrate+Cr2O3 (A)+TiO2 (B)+Al2O3 (C)+TiO2 (D)
substrate+Ti suboxides (A)+TiO2 (B)+SiO2 (C)+TiO2 (D)
substrate+Ti suboxides (A)+TiO2 (B)+Al2O3 (C)+TiO2 (D)
substrate+Fe2O3 (A)+ZrO2 (B)+SiO2 (C)+ZrO2 (D)
substrate+Fe2O3 (A)+ZnO (B)+SiO2 (C)+ZrO2 (D)
substrate+Fe3O4 (A)+ZrO2 (B)+SiO2 (C)+ZrO2 (D)
substrate+Fe3O4 (A)+ZrO2 (B)+SiO2 (C)+TiO2 (D)
substrate+Fe2O3 (A)+TiO2 (B)+SiO2 (C)+ZrO2 (D)
The pigments according to the invention can easily be prepared by the production of an absorption layer and high- and low-refractive-index interference layers with precisely defined thickness and a smooth surface on the finely divided, platelet-shaped substrates.
The metal-oxide layers are preferably applied by wet-chemical methods, it being possible to use the wet-chemical coating methods developed for the production of pearlescent pigments. Methods of this type are described, for example, in DE 14 67 468, DE 19 59 988, DE 20 09 566, DE 22 14 545, DE 22 15 191, DE 22 44 298, DE 23 13 331, DE 25 22 572, DE 31 37 808, DE 31 37 809, DE 31 51 343, DE 31 51 354, DE 31 51 355, DE 32 11 602, DE 32 35 017 or in further patent documents and other publications known to the person skilled in the art.
In the case of wet coating, the substrate particles are suspended in water, and one or more hydrolysable metal salts are added at a pH which is suitable for hydrolysis, the latter being selected in such a way that the metal oxides or metal oxide hydrates are precipitated directly onto the platelets without secondary precipitations occurring. The pH is usually kept constant by simultaneous metering-in of a base or acid. The pigments are subsequently separated off, washed and dried and calcined in a reduced atmosphere, it being possible for the calcination temperature to be optimised with respect to the coating present in each case. In general, the calcination temperatures are between 250 and 900xc2x0 C., preferably between 450 and 700xc2x0 C. If desired, the pigments can be separated off, dried or calcined after application of individual coatings and then re-suspended for precipitation of the further layers.
Coating can furthermore also be carried out in a fluidised-bed reactor by gas-phase coating, it being possible, for example, correspondingly to use the processes proposed in EP 0 045 851 and EP 0 106 235 for the production of pearlescent pigments.
The Fe3O4 layer can be produced, for example, by reduction of the Fe3O4 layer using ammonia, hydrogen or alternatively hydrocarbons and hydrocarbon/ammonia mixtures, as described, for example, in EP-A-0 332 071, DE 19 51 696.8 and DE 19 51 697.7. The reduction is preferably carried out in a forming gas atmosphere (N2/H2), in particular with 92% of N2/8% of H2 or 96% of N2/6% of H2. The reduction temperature is preferably from 400 to 700xc2x0 C., in particular from 500 to 600xc2x0 C.
The colour shade of the pigments can be varied within broad limits by selecting different covering amounts or layer thicknesses resulting therefrom. The fine tuning for a certain colour shade can be achieved beyond the pure choice of amount by approaching the desired colour under visual or measurement technology control.
In order to increase the light, water and weather stability, it is frequently advisable, depending on the area of application, to subject the finished pigment to post-coating or post-treatment. Suitable post-coatings or post-treatments are, for example, the processes described in German Patent 22 15 191, DE-A 31 51 354, DE-A 32 35 017, DE-A 33 34 598, DE 40 30 727 A1, EP 0 649 886 A2, WO 97/29059, WO 99/57204, U.S. Pat. No. 5,759,255. This post-coating (layer E) further increases the chemical stability of the pigments or simplifies handling of the pigment, in particular incorporation into various media.
The pigments according to the invention are compatible with a large number of colour systems, preferably from the area of paints, coatings and printing inks. For the production of printing inks, a large number of binders, in particular water-soluble grades, is suitable, as marketed, for example, by BASF, Marabu, Prxc3x6ll, Sericol, Hartmann, Gebr. Schmidt, Sicpa, Aarberg, Siegberg, GSB-Wahl, Follmann, Ruco or Coates Screen INKS GmbH. The printing inks may be water-based or solvent-based. The pigments are furthermore also suitable for the laser marking of paper and plastics, and for applications in the agricultural sector, for example for greenhouse sheeting, and, for example, for the colouring of tent awnings.
It goes without saying that, for the various applications, the multilayer pigments can also advantageously be used in the form of a mixture with organic dyes, organic pigments or other pigments, such as, for example, transparent and hiding white, coloured and black pigments, and with platelet-shaped iron oxides, organic pigments, holographic pigments, LCPs (liquid crystal polymers) and conventional transparent, coloured and black lustre pigments based on metal oxide-coated mica and SiO2 platelets, etc. The multilayer pigments can be mixed with commercially available pigments and fillers in any ratio.
The pigments according to the invention are furthermore suitable for the production of flowable pigment preparations and dry preparations. The pigment preparations and dry preparations are distinguished by the fact that they comprise one or more pigments according to the invention, binders and optionally one or more additives.
The invention thus also relates to the use of the pigments in formulations such as paints, printing inks, coatings, plastics, ceramic materials, glasses, in cosmetic formulations, for laser marking and for the production of pigment preparations and dry preparations.
In the foregoing and in the following examples, all temperatures are set forth uncorrected in degrees Celsius; and, unless otherwise indicated, all parts and percentages are by weight.
The entire disclosure of all applications, patents and publications, cited above and below, and of corresponding German Application No. DE 101 51 844.7, filed Oct. 24, 2001 is hereby incorporated by reference.
The following examples are intended to explain the invention in greater detail, but without restricting it.